Honeycomb structure

ABSTRACT

This is directed to a honeycomb structure ( 10 ) including two or more honeycomb segments ( 11 ) having numerous through channels having been partitioned by walls and penetrating in axial direction thereof, the walls for through channels having a filtering function, and one end being clogged at predetermined through channels, and the other end at the remaining ones, and joint layers ( 12 ) for joining two or more honeycomb segments ( 11 ) each other. It may satisfy at least either that the Young&#39;s modulus of material of the joint layer ( 12 ) is 20% or less of that of the honeycomb segment ( 11 ), or that the material strength of joint layer ( 12 ) is lower than that of the honeycomb segment ( 11 ). This honeycomb structure shows a less thermal stress during use, has such a durability that no crack is formed, hardly shows a difference in temperature between the central portion and outer peripheral portion, and shows a lower pressure loss of fluid.

TECHNICAL FIELD

[0001] The present invention relates to a honeycomb structure used as afilter which collects and removes particulate matters exhausted in aheat engine such as an internal combustion engine or combustionequipment such as a boiler.

BACKGROUND ART

[0002] Conventionally, as a method for collecting and removingparticulate matters contained in a dust-containing fluid such as exhaustgas emitted from a diesel engine or the like, there is known the use ofa honeycomb structure in which a wall of through channel has a filteringfunction, one end is clogged for predetermined through channels, and theother end is clogged for the remaining through channels.

[0003] In the case where such a honeycomb structure is used as a filterfor collecting particulate matters in exhaust gas, it is necessary toperform regenerating treatment in which accumulating carbon particulatesare burned and removed. At this time, a local increase in temperature isunavoidable, so that a high thermal stress is liable to occur, whichposes a problem in that a crack is liable to develop.

[0004] As measures for reducing the thermal stress occurring in such astructural part, a method in which the structural part is divided intosmall segments is known. The use of a honeycomb structure for collectingparticulates in exhaust gas has already been proposed in JP-A-6-241017,JP-A-8-28246, JP-A-7-54643, JP-A-8-28248, etc.

[0005] However, even in the examples proposed in the aforementionedpatent publications, the effect of reducing stress on segment surface isinsufficient, and the problem of crack development cannot be solvedcompletely. Also, there is a problem in that a shift in axial directionoccurs between the segments during the use. Although a method in which aholding member is used to prevent the shift in the axial direction hasbeen proposed in JP-A-6-241017, there is a problem of deformation anddeterioration of the holding member occurring when the member is subjectto high temperatures of exhaust gas.

[0006] As other measures for reducing thermal stress, there has beenproposed a method in which a portion liable to have a relatively lowtemperature is heated electrically by providing an electric heaterbetween the segments to make the temperature distribution in honeycombstructure uniform. However, this method has a problem of the occurrenceof a new thermal stress because a local temperature gradient ratherincreases in the vicinity of the electric heater.

[0007] Also, there are a problem in that the ratio of the joint layerbetween the segments to the cross section is too high, so that thepressure loss of fluid is excessive, which deteriorates the engineperformance, and a problem in that the heat capacity is too high, sothat the rise in temperature takes much time in the regeneratingtreatment in which carbon particulates are burned to be removed, whichprolongs the time necessary for regenerating treatment.

[0008] The present invention has been made to solve the above problems,and accordingly an object thereof is to provide a honeycomb structure inwhich a less thermal stress occurs during the use; durability such thatno crack develops is ensured; a difference in temperature between thecentral portion and the outer peripheral portion is less liable to beproduced; the pressure loss of fluid is low; and the time and energynecessary for the rise in temperature at the time of regeneratingtreatment are less.

DISCLOSURE OF THE INVENTION

[0009] According to the present invention, there is provided a honeycombstructure including two or more honeycomb segments each of which has alarge number of through channels which are partitioned by walls andpenetrate in the axial direction, the wall of the through channel havinga filtering function, and is constructed so that one end is clogged forpredetermined through channels, and the other end is clogged for theremaining through channels, and a joint layer for joining the two ormore honeycomb segments to each other, characterized in that at leasteither that the Young's modulus of material of the joint layer is 20% orless of the Young's modulus of material of the honeycomb segment, orthat the material strength of the joint layer is lower than the materialstrength of the honeycomb segment is satisfied.

[0010] In the present invention, a portion having an area of at least30% of the surface area of the honeycomb segment in contact with thejoint layer preferably has average surface roughness Ra exceeding 0.4micron, and the ratio of the total heat capacity of all the joint layersin the honeycomb structure to the total heat capacity of all thehoneycomb segments constituting the honeycomb structure is preferably30% or lower.

[0011] Further, in the honeycomb structure in accordance with thepresent invention, it is preferable that a corner portion of across-sectional shape of the honeycomb segment in the cross sectionperpendicular to the through channel of the honeycomb structure berounded with a radius of curvature of 0.3 mm or larger, or be chamfered0.5 mm or more.

[0012] Also, the ratio of the total cross-sectional area of the jointlayers to the cross-sectional area of the honeycomb structure in thecross section perpendicular to the through channel of the honeycombstructure is preferably 17% or lower, and further the ratio of the sumof the cross-sectional areas of the joint layers to the sum of thecross-sectional areas of the walls in the cross section of honeycombstructure perpendicular to the through channel of the honeycombstructure is preferably 50% or lower. Sill further, it is preferablethat the ratio of the cross-sectional area of joint layer to thecross-sectional area of wall in the cross section of honeycomb structureperpendicular to the through channel of the honeycomb structure behigher in the central portion and be lower on the outer peripheral side.

[0013] As a material of the honeycomb segment, one kind of materialselected from a group consisting of cordierite, SiC, SiN, alumina,mullite, and lithium aluminum silicate (LAS) is preferably used as amain crystal phase from the viewpoint of strength, heat resistance, andthe like.

[0014] Also, it is preferable that the honeycomb segment carry a metalhaving a catalytic function so as to be used to purify exhaust gas froma heat engine or combustion equipment or to reform a liquid fuel or agas fuel. As the metal having a catalytic function, at least one kind ofPt, Pd, and Rh is preferably used.

[0015] Further, the cross-sectional shape of the through channel in thehoneycomb structure is preferably any of triangle, quadrangle, andhexagon.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIGS. 1(a), 1(b), 1(c) and 1(d) are explanatory views showingvarious division patterns of honeycomb segment of a honeycomb structurein accordance with the present invention.

[0017]FIG. 2 is a partially enlarged view showing a cell construction ofa honeycomb structure.

[0018]FIG. 3 is a sectional view for illustrating one example of ahoneycomb structure.

[0019]FIG. 4 is a partially enlarged view showing a cell constructionand a joint layer of a honeycomb structure.

[0020]FIG. 5 is a perspective view showing one example of a test piececut out of a honeycomb structure.

[0021]FIG. 6 is an explanatory view showing an example of a four-pointbending test.

BEST MODE FOR CARRYING OUT THE INVENTION

[0022] The present invention will now be described in further detailwith reference to an embodiment shown in the accompanying drawings. Thepresent invention is not limited to this embodiment.

[0023] FIGS. 1(a), 1(b), 1(c) and 1(d) are explanatory views showingvarious division patterns of honeycomb segment of a honeycomb structurein accordance with the present invention.

[0024] In FIGS. 1(a), 1(b), 1(c) and 1(d), reference numeral 10 denotesa honeycomb structure. The honeycomb structure 10 is made up of two ormore honeycomb segments 11 and joint layers 12 for joining thesehoneycomb segments 11. Though not shown in detail, the honeycomb segment11 has a large number of through channels 15 which are partitioned bywalls 14 and penetrate in the axial direction. The wall 14 of thethrough channel 15 has a filtering function, and the construction issuch that one end is clogged for predetermined through channels 15, andthe other end is clogged for the remaining through channels 15.

[0025] In the honeycomb structure in accordance with the presentinvention, the Young's modulus of a material forming the joint layer 12is made preferably 20% or less more preferably 1% or less of the Young'smodulus of a material forming the honeycomb segment 11, or the materialstrength of the joint layer 12 is made lower than the material strengthof the honeycomb segment 11. By specifying the Young's moduli ofmaterials of the joint layer 12 and the honeycomb segment 11, ahoneycomb structure in which a less thermal stress occurs during theuse, and durability such that no crack develops is ensured can beprovided. Also, even in the case where the Young's modulus of the jointlayer 12 exceeds 20% of the Young's modulus of the honeycomb segment 11,if the material strength of the joint layer 12 is lower than thematerial strength of the honeycomb segment 11, a crack develops only inthe joint layer 12, and the honeycomb segment 11 is not damaged, so thatthe honeycomb structure maintains a sufficient function.

[0026] Herein, the Young's modulus of the joint layer 12 and the Young'smodulus of the honeycomb segment 11 means the Young's modulus of eachmaterial itself thereof, that is, the physical property inherent in thematerial.

[0027] Also, the definition of “the material strength of the joint layeris lower than the material strength of the honeycomb segment” will beexplained below with reference to FIGS. 5 and 6.

[0028] A test piece 20 cut out of the honeycomb structure in accordancewith the present invention as shown in FIG. 5 is prepared. The testpiece 20 is cut so that the length in the direction perpendicular to thethrough channel is 40 mm or larger and the joint layer 12 is located inthe center thereof. In the present invention, the fact that in afour-point bending test (in conformity to JIS R1601) as shown in FIG. 6of the test piece 20, the probability that a fracture occurs within thejoint layer 12 or at the interface between the joint layer 12 and thehoneycomb segment 11 is 50% or higher is defined as the aforementioned“the material strength of the joint layer is lower than the materialstrength of the honeycomb segment”.

[0029] Also, it is preferable that in this honeycomb structure, aportion having an area of at least 30% of the surface area of thehoneycomb segment 11 in contact with the joint layer 12 have averagesurface roughness Ra exceeding 0.4 micron. Thereby, the two or morehoneycomb segments 11 are joined more firmly, and a fear of peeling offat the time of use can almost be dispelled. The aforementioned surfaceroughness Ra is further preferably be 0.8 microns or more.

[0030] Also, the ratio of the total heat capacity of all the jointlayers in the honeycomb structure to the total heat capacity of all thehoneycomb segments constituting the honeycomb structure is preferablymade 30% or lower, more preferably 15% or lower. Thereby, when thecarbon particulates collected at the time of regeneration are burned tobe disposed of (filter regeneration), the time taken for the rise intemperature can desirably be kept in the allowable range.

[0031] Further, it is preferable that in the honeycomb structure inaccordance with the present invention, a corner portion of across-sectional shape of honeycomb segment in the cross sectionperpendicular to the through channel of honeycomb structure be roundedwith a radius of curvature of 0.3 mm or larger, or be chamfered 0.5 mmor more because the occurrence of thermal stress at the time of use isreduced and great durability such that no crack develops can be given tothe honeycomb structure.

[0032] Still further, in the present invention, it is preferable thatthe ratio of the total cross-sectional area of the joint layers to thecross-sectional area of the honeycomb structure in the cross sectionperpendicular to the through channel of honeycomb structure be 17% orlower, more preferably 8% or lower. The explanation of this is givenwith reference to FIG. 3. Referring to FIG. 3, in the circular honeycombstructure 10 having a cross section with diameter D, the totalcross-sectional area S_(H) of the honeycomb structure 10 is expressed bythe following formula.

S _(H)=(π/4)×D ²

[0033] On the other hand, the total cross-sectional area S_(s) of thejoint layers 12 is the total area of hatched portion A in FIG. 3(cross-sectional portion of the joint layers 12).

[0034] Herein, the ratio of S_(S)/S_(H) should preferably be 17% orlower from the viewpoint of the decrease in pressure loss of fluid.

[0035] Also, in the present invention, it is preferable that the ratioof the sum of the cross-sectional areas of joint layers to the sum ofthe cross-sectional areas of walls in the cross section of honeycombstructure perpendicular to the through channel of honeycomb structure be50% or lower, more preferably 24% or lower. Referring to FIG. 4, takingthe sum of the cross-sectional areas (hatched portion B) of the jointlayers 12 in the cross section of the honeycomb structure 10 as S_(s),and taking the sum of the cross-sectional areas (meshed portion C) ofthe walls 14 as S_(c), the ratio of S_(s)/S_(c) should preferably be 50%or lower from the viewpoint of the decrease in pressure loss of fluid.

[0036] Further, in the present invention, it is preferable that theratio of the cross-sectional area of joint layer to the cross-sectionalarea of wall in the cross section of honeycomb structure perpendicularto the through channel of honeycomb structure be higher in the centralportion and be lower on the outer peripheral side. According to suchconfiguration, the quantity of collected carbon particulates per unitvolume is smaller in the vicinity of the center than in the vicinity ofthe outer periphery, so that at the time of regenerating treatment atwhich carbon particulates are burned (regenerative combustion time), thecalorific value in the vicinity of the center, where high temperaturesare liable to be generated, can be kept low. Moreover, the joint layerin the vicinity of the center is dense, so that the heat capacity inthat portion can be increased. For these reasons, the increase intemperature in the vicinity of the center can be kept low. As a result,a difference in temperature between the central portion and the outerperipheral side can be decreased, so that the thermal stress in thehoneycomb structure can desirably be decreased.

[0037] In the present invention, the cross section perpendicular to thethrough channel of honeycomb structure can take various shapes such ascircle, ellipse, and racetrack.

[0038] Also, the honeycomb segment constituting the honeycomb structurein accordance with the present invention preferably has a main crystalphase of one kind selected from a group consisting of cordierite, SiC,SiN, alumina, mullite, and lithium aluminum silicate (LAS) from theviewpoint of strength, heat resistance, and the like. Silicon carbide(SiC), which has a high coefficient of thermal conductivity, isespecially preferable because heat can be dissipated easily.

[0039] The cell density of honeycomb segment is preferably 6 to 1500cells/in² (0.9 to 233 cells/cm²), further preferably 50 to 400 cells/in²(7.8 to 62 cells/cm²). If the cell density is lower than 6 cells/in²,the strength and effective GSA (Geometrical Surface Area) areinsufficient as the honeycomb segment. If the cell density is higherthan 1500 cells/in², the pressure loss increases when gas flows.

[0040] Also, the cross-sectional shape of through channel (cell shape)in the honeycomb structure is preferably any of triangle, quadrangle,and hexagon from the viewpoint of manufacture.

[0041] Also, as a material of joint layer that joins the honeycombsegment to each other, ceramic fiber, ceramic powder, cement, or thelike, which has heat resistance, are preferably used singly or by beingmixed. Further, as necessary, an organic binder, an inorganic binder,etc. may be used by being mixed. The material of joint layer is notlimited to the above-described materials.

[0042] The honeycomb structure in accordance with the present inventionhas a construction such that, as described above, it has a large numberof through channels which are partitioned by walls and penetrate in theaxial direction; the wall of the through channel has a filteringfunction; and one end is clogged for predetermined through channels, andthe other end is clogged for the remaining through channels. Therefore,the honeycomb structure can be suitably used as a filter which collectsand removes particulate matters contained in a dust-containing fluid,such as a particulate filter for a diesel engine.

[0043] Specifically, if a dust-containing fluid is caused to passthrough one end face of the honeycomb structure having such aconstruction, the dust-containing fluid enters a through channel in thehoneycomb structure whose end on the one end face side is not clogged,and passes through the porous wall having a filtering function to enteranother through channel in the honeycomb structure whose end on theother end face side is not clogged. When passing through the wall,particulate matters in the dust-containing fluid are collected to thewall, and the purified fluid from which particulate matters have beenremoved is discharged from the other end face of honeycomb structure.

[0044] If the collected particulate matters accumulate on the wall, thewall is clogged, so that the function as a filter decreases. Therefore,the honeycomb structure is heated periodically by heating means such asa heater to burn and remove the particulate matters, by which thefiltering function is regenerated. To accelerate the combustion ofparticulate matters at the time of regeneration, a metal having acatalytic function, as described later, may be carried on the honeycombsegment.

[0045] On the other hand, in the case where the honeycomb structure inaccordance with the present invention is used to purify exhaust gas froma heat engine such as an internal combustion engine or to reform aliquid fuel or a gas fuel as a catalyst carrier, a metal having acatalytic function is carried on the honeycomb segment. As a typicalmetal having a catalytic function, Pt, Pd, and Rh are cited. At leastone kind of these metals is preferably carried on the honeycomb segment.

[0046] Hereunder, the present invention will be described in furtherdetail with reference to examples. The present invention is not limitedto these examples.

EXAMPLES 1 to 10, COMPARATIVE EXAMPLE 1

[0047] Honeycomb structures measuring 144 mm in diameter and 153 mm inlength having various division constructions were manufactured using aSiC-made honeycomb segment having a wall thickness of 0.38 mm, a celldensity of 200 cells/in² (31 cells/cm²), and a thickness of outerperipheral portion of 0.5 mm, and using a mixture of ceramic fiber,ceramic powder, and organic and inorganic binders as the joint layer.The division construction and the properties such as the Young's modulusof material of the obtained honeycomb structure are given in Table 1.Also, the surface roughness given in Table 1 indicates the averagesurface roughness of the whole surface of honeycomb segment in contactwith the joint layer.

[0048] This honeycomb structure is a particulate filter for purifyingexhaust gas from a diesel engine, which has a construction such that oneend is clogged for predetermined through channels, and the other end isclogged for the remaining through channels. The fluid pressure loss testand the regeneration test were conducted on these honeycomb structures.The results are given in Table 1. TABLE 1 Example 1 Example 2 Example 3Example 4 Example 5 Example 6 Division construction (a) (b) (b) (b) (c)(c) Young's modulus of wall 42 42 42 42 42 42 material (Gpa) Young'smodulus of joint 0.4 4 4 4 8 8 layer material (Gpa) Young's modulus ofjoint layer/Young's modulus of 1 10 10 10 19 19 wall (%) Segment cornerR0.3 Acute R0.3 R0.3 R0.3 R0.3 angle Result of Quantity of AbsentPresent Present Present Present Present regeneration soot: Large test(segment Quantity of Absent Present Absent Absent Absent Absent crack)soot: Standard Segment surface roughness (Ra 0.8 0.8 0.3 0.3 0.8 0.8 μm)Absent Absent Present Present Absent Absent Axial shift after test Wallthickness (mm) 0.38 0.38 0.38 0.38 0.38 0.38 Joint layer thickness (mm)2 2 2 2 4 2 Joint layer area/structure 3.5 4.4 4.4 4.4 17 8.5 area (%)Joint layer area/wall area (%) 9.7 12.2 12.2 12.2 50 24.5 Result offluid pressure loss Allowable Allowable Allowable Allowable AllowableAllowable test range range range range range range Regeneration timeAllowable Allowable Allowable Allowable Allowable Allowable range rangerange range range range Heat capacity ratio (%) 6 7 7 7 30 15 Jointlayer strength (with respect to segment strength) High High High HighHigh High Comparative Example 7 Example 8 Example 9 Example 10 example 1Division construction (c) (d) (c) (c) Integrated product Young's modulusof wall 42 42 42 42 42 material (Gpa) Young's modulus of joint 8 4 30 30— layer material (Gpa) Young's modulus of joint 19 10 71 71 —layer/Young's modulus of wall (%) Segment corner R0.3 R0.3 R0.3 R0.3 —Result of Quantity of Present Present Absent Absent Present regenerationsoot: Large test (segment Quantity of Absent Absent Absent AbsentPresent crack) soot: Standard Segment surface roughness (Ra 0.8 0.8 0.80.8 — μm) Absent Absent Present Absent — Axial shift after test Wallthickness (mm) 0.38 0.38 0.38 0.38 0.38 Joint layer thickness (mm) 5 2 12 2 Joint layer area/structure 21 5.3 4.3 8.5 — area (%) Joint layerarea/wall area (%) 70.5 14.7 12.3 24.5 — Result of fluid pressure lossHigh Allowable Allowable Allowable Allowable test range range rangerange Regeneration time Long Allowable Allowable Allowable Allowablerange range range range Heat capacity ratio (%) 42 9 8 15 — Joint layerstrength (with respect to segment strength) High High Low Low —

[0049] [Evaluation]

[0050] As is apparent from the results given in Table 1, when therequirements specified in the present invention were satisfied, thepressure loss of fluid was not so high, being within the allowable range(10 kPa), and the regeneration time was within the allowable range (15min).

[0051] Industrial Applicability

[0052] As described above, the honeycomb structure in accordance withthe present invention achieves a remarkable effect that a less thermalstress occurs during the use; durability such that no crack develops isensured; a difference in temperature between the central portion and theouter peripheral portion hardly occurs; and moreover the pressure lossof fluid is low.

1. A honeycomb structure comprising two or more honeycomb segments eachof which has a large number of through channels which are partitioned bywalls and penetrate in axial directions, the wall of said throughchannel having a filtering function, and is constructed so that one endis clogged for predetermined through channels, and the other end isclogged for the remaining through channels, and a joint layer forjoining said two or more honeycomb segments to each other, characterizedin that either that the Young's modulus of material of said joint layeris 20% or less of the Young's modulus of material of said honeycombsegment, or that the material strength of said joint layer is lower thanthe material strength of said honeycomb segment is satisfied.
 2. Thehoneycomb structure according to claim 1, characterized in that aportion having an area of at least 30% of the surface area of saidhoneycomb segment in contact with said joint layer has an averagesurface roughness Ra exceeding 0.4 micron.
 3. The honeycomb structureaccording to claim 1 or 2, characterized in that the ratio of the totalheat capacity of all the joint layers in said honeycomb structure to thetotal heat capacity of all the honeycomb segments constituting saidhoneycomb structure is 30% or lower.
 4. The honeycomb structureaccording to any one of claims 1 to 3, characterized in that a cornerportion of the cross-sectional shape of said honeycomb segment in across section perpendicular to the through channel of said honeycombstructure is rounded with a radius of curvature of 0.3 mm or larger, oris chamfered 0.5 mm or more.
 5. The honeycomb structure according to anyone of claims 1 to 4, characterized in that the ratio of the totalcross-sectional area of said joint layers to the cross-sectional area ofsaid honeycomb structure in a cross section perpendicular to the throughchannel of said honeycomb structure is 17% or lower.
 6. The honeycombstructure according to any one of claims 1 to 5, characterized in thatthe ratio of the sum of the cross-sectional areas of said joint layersto the sum of the cross-sectional areas of said walls in a cross sectionof honeycomb structure perpendicular to the through channel of saidhoneycomb structure is 50% or lower.
 7. The honeycomb structureaccording to any one of claims 1 to 6, characterized in that saidhoneycomb segment has a main crystal phase of one kind selected from agroup consisting of cordierite, SiC, SiN, alumina, mullite, and lithiumaluminum silicate (LAS).
 8. The honeycomb structure according to any oneof claims 1 to 7, characterized in that said honeycomb segment carries ametal having a catalytic function so as to be used to purify exhaust gasfrom a heat engine or combustion equipment or to reform a liquid fuel ora gas fuel.
 9. The honeycomb structure according to claim 8,characterized in that said metal having a catalytic function is at leastone kind of Pt, Pd, and Rh.
 10. The honeycomb structure according to anyone of claims 1 to 9, characterized in that the cross-sectional shape ofsaid through channel in said honeycomb segment is any of triangle,quadrangle, and hexagon.